US7868561B2 - Two-wire dimmer circuit for a screw-in compact fluorescent lamp - Google Patents

Abstract

A dimmer switch for controlling the intensity of a dimmable screw-in compact fluorescent lamp provides smooth dimming of the fluorescent lamp and prevents flickering of the lamp due to multiple re-strikes. The dimmer switch prevents multiple re-strikes by avoiding multiple firings of a controllably conductive switching device of the dimmer circuit by limiting the high-end light intensity of the fluorescent lamp. Specifically, the dimmer switch limits the length of a conduction interval of the controllably conductive switching device to less than approximately 75% of each half-cycle. The dimmer switch may include a user-accessible adjustment actuator for changing the dimmer switch between an incandescent operating mode and a screw-in compact fluorescent mode. The dimmer switch may also be operable to automatically change the dimmer switch between the incandescent operating mode and the screw-in compact fluorescent mode by detecting the occurrence of the multiple firings of the controllably conductive switching device.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to load control devices for controlling the amount of power delivered to an electrical load from a power source. More specifically, the present invention relates to a two-wire dimmer circuit for controlling the intensity of a dimmable screw-in compact fluorescent lamp.

2. Description of the Related Art

A conventional two-wire dimmer circuit10, as shown inFIG. 1, has two terminals: a “hot” terminal H for connection to an alternating-current (AC) power source12 (e.g., 120 V_AC@60 Hz) and a “dimmed hot” terminal DH for connection to alighting load14, such as an incandescent lamp. Thedimmer circuit10 typically uses a bi-directional semiconductor switch (not shown), such as, for example, a triac, to control the current delivered to thelighting load14, and thus to control the state (i.e., on or off) and the intensity of the lighting load between a high-end intensity setting (i.e., a maximum value) and a low-end intensity setting (i.e., a minimum value). The bi-directional semiconductor switch is typically coupled between the hot terminal H and the dimmed hot terminal DH of thedimmer circuit10, and thus, in series between theAC power source12 and thelighting load14. The bi-directional semiconductor switch is controlled to be conductive and non-conductive each half-cycle to control the amount of power delivered to thelighting load14.

FIG. 2A is a simplified diagram of a hot voltage V_Hreceived from the AC power source12 (as shown by the dotted line) and a dimmed-hot voltage V_DHprovided to thelighting load14 when thedimmer circuit10 is controlling the intensity of the lighting load to the high-end intensity setting.FIG. 2B is a simplified diagram of the hot voltage V_Hand the dimmed-hot voltage V_DHwhen thedimmer circuit10 is controlling the intensity of thelighting load14 to the low-end intensity setting. Using a forward phase control (or “phase-cut”) dimming technique, thedimmer circuit10 controls the semiconductor switch to be non-conductive at the beginning of each half-cycle of theAC power source12 during an off time T_OFF. Then, thedimmer circuit10 renders the semiconductor switch conductive during a conductive interval T_CON(i.e., an on time) after the off time T_OFF. Thedimmer circuit10 maintains the semiconductor switch conductive during the conduction interval T_CONuntil the end of the half-cycle. The intensity of thelighting load14 is dependent upon how long the semiconductor switch is conductive each half-cycle. At the high-end intensity setting, the off time T_OFFis approximately 1.4 msec, such that the conduction interval T_CONis approximately 6.9 msec (assuming that each half-cycle is approximately 8.3 msec long on a 120-V_AC, 60-Hz AC power source12). At the low-end intensity setting, the off time T_OFFis approximately 6.8 msec, such that the conduction interval T_CONis approximately 1.5 msec. Forward phase control dimming is typically used to control incandescent and magnetic low-voltage (MLV) lighting loads.

Gas discharge lamps, such as fluorescent lamps, must be driven by a ballast in order to illuminate properly.FIG. 3 is a simplified block diagram of a lighting system including a fluorescent Tu-Wire®dimmer circuit20 for driving a two-wirefluorescent load24. Thefluorescent load24 only requires two connections, i.e., to the dimmed hot terminal DH of the fluorescent Tu-Wire®dimmer circuit20 and to the neutral of theAC power source12. Thefluorescent load24 includes a two-wire ballast26 (e.g., a Tu-Wire® electrical dimming ballast, part number 2W-T418-120-2-S, manufactured by Lutron Electronics Co., Inc., or a Mark X® electrical dimming ballast manufactured by Advance Transformer Co.) and afluorescent lamp28. Because of the size of theballast26, the ballast is typically located in a junction box external to the lighting fixture of thefluorescent lamp28. Theballast26 includes a full-wave rectifier for receiving the dimmed-hot voltage from thedimmer circuit20, and an active front-end, such as a boost converter, for generating a substantially direct-current (DC) bus voltage. A back-end of theballast26 converts the DC bus voltage to a high-frequency AC voltage for driving thefluorescent lamp28.

The Tu-Wire®dimmer circuit20 is specifically designed to drive thefluorescent load24 and may comprise part number NTFTU-5A or part number SFTU-5A3P, both manufactured by Lutron Electronics Co., Inc. Theballast26 controls the intensity of thelamp28 in response to the amount of time that the semiconductor switch of thedimmer circuit20 is conductive each half-cycle. Theballast26 requires a minimum input voltage greater than the minimum input voltage of an incandescent lamp or an MLV load, so that the low-end intensity setting of the Tu-Wire®dimmer circuit20 is higher than the low-end intensity setting of thedimmer circuit10 ofFIG. 1 and the lamp does not drop out (i.e., the lamp arc is not extinguished) if the length of the conductive interval T_CONis controlled to be too short. Further, because theballast26 does not draw as much current as an incandescent lamp or an MLV load, the Tu-Wire®dimmer circuit20 includes a bi-directional semiconductor switch having a lower holding current rating than the triac of theincandescent dimmer circuit10 ofFIG. 1. Ideally, the triac of the Tu-Wire®dimmer circuit20 has a holding current rating of approximately 15 mA, where the triac of theincandescent dimmer circuit10 has a holding current rating of approximately 50 mA.

FIG. 4A is a simplified diagram of the hot voltage V_Hand the dimmed-hot voltage V_DHprovided to thefluorescent load24 when the Tu-Wire®dimmer circuit20 is controlling the intensity of thefluorescent lamp28 to the high-end intensity setting.FIG. 4B is a simplified diagram of the hot voltage V_Hand the dimmed-hot voltage V_DHwhen the Tu-Wire®dimmer circuit20 is controlling the intensity of thefluorescent lamp28 to the low-end intensity setting. As shown inFIG. 4A, the high-end intensity setting is the same as the high-end intensity setting of theincandescent dimmer circuit10 ofFIG. 1 (i.e., the off time T_OFFis approximately 1.4 msec). Decreasing the high-end intensity setting of the Tu-Wire®dimmer circuit20 would unnecessarily limit the maximum light output of thefluorescent lamp28. However, the low-end intensity setting of the Tu-Wire®dimmer circuit20 is higher than that provided by thedimmer circuit10 ofFIG. 1. Specifically, the Tu-Wire®dimmer circuit20 provides a maximum off time T_OFFof approximately 5.6 msec, such that the semiconductor switch is conductive for approximately 2.75 msec each half-cycle, i.e., at least approximately 33% of each half-cycle. The maximum off time T_OFFmay range from approximately 5.4 to 5.7 milliseconds (i.e., approximately 31%-35% of each half-cycle) resulting in the dimmed hot voltage V_DHhaving a magnitude of approximately 50 to 58 V_RMSwhen thedimmer circuit20 is controlling the intensity of thefluorescent lamp28 to the low-end intensity setting.

Recently, compact fluorescent lamps that comprise screw-in bases for attachment to standard Edison sockets have become popular replacements for standard screw-in incandescent bulbs. These screw-in compact fluorescent lamps consume less power than incandescent bulbs and provide an easy solution for reducing the power consumption of a lighting system. The screw-in compact fluorescent lamps have an integral ballast circuit housed in the base of the lamp and are often made to look similar to incandescent lamps, such as BR30 lamps and PAR38 lamps. Since the screw-in compact fluorescent lamps have different operational characteristics than incandescent lamps, the dimmer circuits used for the screw-in incandescent lamps (as shown inFIG. 1) are not able to appropriately control the screw-in compact fluorescent lamps.

Particularly, problems often arise when the Tu-Wire®dimmer circuit20 attempts to control the intensity of a dimmable screw-in compact fluorescent lamp to the high-end intensity setting.FIG. 5 is a simplified block diagram of the Tu-Wire®dimmer circuit20 controlling a dimmable screw-in compact fluorescent lamp34 (e.g., a Philips® Marathon® dimmable screw-in compact fluorescent lamp), which includes aballast circuit36, located in a base portion, and acoil lamp tube38.FIG. 6 is a simplified diagram of the hot voltage V_Hand the dimmed-hot voltage V_DHprovided to the screw-influorescent lamp34 when the Tu-Wire®dimmer circuit20 is attempting to control the intensity of the fluorescent lamp to the high-end intensity setting. When thedimmer circuit20 attempts to fire the triac near the beginning of the half-cycle when the hot voltage V_His still relatively small, the screw-influorescent lamp34 may not draw enough current to exceed the latching current rating and/or the holding current rating of the triac in the Tu-Wire®dimmer circuit20. Therefore, the Tu-Wire®dimmer circuit20 attempts to fire the semiconductor switch multiple times (as shown bymultiple voltage peaks40 inFIG. 6) until the semiconductor switch is finally rendered conductive. These multiple firings of the semiconductor switch can cause flicker in the light output, audible noise, increased electro-magnetic interference (EMI), and excessive stress on the components of thedimmer circuit20 and theballast circuit36 of the screw-in fluorescent lamp. As a result, the dimming of compact fluorescent lamps has been commercially unsuccessful thus reducing the possibility of further energy savings with these desirable replacements for energy-wasting incandescent lamps.

Therefore, there is a need for a dimmer circuit that provides smooth dimming of a screw-in compact fluorescent lamp and avoids the issues of multiple firings of the semiconductor switch.

SUMMARY OF THE INVENTION

According to the present invention, a two-wire dimmer control circuit for a dimmable screw-in compact fluorescent lamp load comprises a controllably conductive switching device, a phase-cut AC drive circuit, and a high-end intensity regulation circuit. The controllably conductive switching device has a control electrode and is adapted to be coupled in series electrical connection between an AC power source and a ballast circuit of the screw-in fluorescent lamp load. The phase-cut AC drive circuit is connected to the control electrode of the controllably conductive switching device for rendering the controllably conductive switching device conductive for a conductive interval each half-cycle of the AC power source. The phase-cut AC drive circuit is operable to control the length of the conduction interval of the controllably conductive switching device each half-cycle. The high-end intensity regulation circuit limits the length of the conduction interval of the controllably conductive switching device to less than approximately 75% of each half-cycle, thereby preventing multiple firings of the controllably conductive switching device.

The present invention further provides a phase-cut circuit for controlling the amount of power delivered from an AC power source to an incandescent lamp. The phase-cut circuit is modified to drive a fluorescent ballast for a fluorescent lamp. The phase-cut circuit includes a triac that has a lower holding current than that used for the incandescent lamp, and provides a reduced high end as compared to that used for the incandescent lamp.

According to another embodiment of the present invention, a two-wire dimmer circuit for a fluorescent lamp load comprises a bi-directional semiconductor switch, a timing circuit, and a trigger circuit for rendering the bi-directional semiconductor switch conductive for a conduction interval each half-cycle, where the improvement comprises the timing circuit being adapted to limit the conduction interval to less than approximately 75% of each half-cycle. The bi-directional semiconductor switch is adapted to be coupled in series electrical connection between the AC power source and a ballast circuit of the fluorescent lamp for controlling the amount of power delivered to the ballast circuit. The timing circuit is operatively coupled in parallel electrical connection with the bi-directional semiconductor switch, and has an output for generating a timing voltage representative of a desired intensity of the fluorescent lamp. The trigger circuit is operatively coupled between the output of the timing circuit and a control input of the bi-directional semiconductor switch. The trigger circuit is operable to render the bi-directional semiconductor switch conductive in response to the timing voltage, such that the bi-directional semiconductor switch is conductive for the conduction interval each half-cycle.

In addition, the present invention provides a two-wire dimmer control circuit for a fluorescent lamp load comprising means for conducting a load current from an AC power source to a ballast circuit of the fluorescent lamp load for a conduction interval each half-cycle of the AC power source, and means for controlling the length of the conduction interval each half-cycle. The improvement comprises means for limiting the length of the conduction interval to less than approximately 75% of each half-cycle.

The present invention further provides a method of controlling a fluorescent lamp load including a ballast circuit. The method comprising the steps of: (1) conducting a load current from an AC power source to the ballast circuit for a conduction interval each half-cycle of the AC power source; (2) controlling the length of the conduction interval each half-cycle; and (3) limiting the length of the conduction interval to less than approximately 75% of each half-cycle.

According to another aspect of the present invention, a dimmer switch is adapted to be coupled between an AC power source generating an AC line voltage and a lighting load for controlling the intensity of the lighting load between a high-end intensity setting and a low-end intensity setting. The dimmer switch comprises a controllably conductive switching device adapted to be coupled in series electrical connection between the AC power source and the lighting load for controlling the amount of power delivered to the lighting load, a drive circuit coupled to a control input of the controllably conductive switching device for controlling the controllably conductive switching device to be conductive for a conduction interval each half-cycle of the AC power source, and a user interface operable to receive a user input for changing the dimmer switch between first and second operating modes. The drive circuit is operable to adjust the high-end intensity setting to a first high-end intensity setting value and the low-end intensity setting to a first low-end intensity setting value in the first operating mode, and to adjust the high-end intensity setting to a second high-end intensity setting value and the low-end intensity setting to a second low-end intensity setting value in the second operating mode. Preferably, the second high-end intensity setting value is less than the first high-end intensity setting value, and the second low-end intensity setting value is greater than the first low-end intensity setting value.

According to another embodiment of the present invention, a dimmer switch for controlling the intensity of a lighting load between a high-end intensity setting and a low-end intensity setting comprises a user-accessible adjustment actuator for changing the dimmer switch between first and second operating modes. The high-end intensity setting is adjusted to a first high-end intensity setting value and the low-end intensity setting is adjusted to a first low-end intensity setting value in the first operating mode, and the high-end intensity setting is adjusted to a second high-end intensity setting value and the low-end intensity setting is adjusted to a second low-end intensity setting value in the second operating mode.

According to another embodiment of the present invention, a dimmer switch for controlling the intensity of a lighting load between a high-end intensity setting and a low-end intensity setting comprises a controllably conductive switching device, a controller, and a user interface. The controllably conductive switching device is adapted to be coupled in series electrical connection between an AC power source and the lighting load for controlling the amount of power delivered to the lighting load. The controller is coupled to a control input of the controllably conductive switching device for controlling the controllably conductive switching device to be conductive for a conduction interval each half-cycle of the AC power source. The controller is operable to change the dimmer switch between first and second operating modes in response a user input received by the user interface. The high-end intensity setting is adjusted to a first high-end intensity setting value and the low-end intensity setting is adjusted to a first low-end intensity setting value in the first operating mode, and the high-end intensity setting is adjusted to a second high-end intensity setting value and the low-end intensity setting is adjusted to a second low-end intensity setting value in the second operating mode.

The present invention further provides a drive circuit for a controllably conductive switching device of a dimmer switch for controlling the intensity of a lighting load between a high-end intensity setting and a low-end intensity setting. The drive circuit comprises a potentiometer for providing a variable resistance, a firing capacitor coupled to an output of the potentiometer for generating a timing voltage, and a mechanical switch for changing the dimmer switch between first and second operating modes. The firing capacitor is adapted to charge through the potentiometer such that the timing voltage is responsive to the variable resistance of the potentiometer. The high-end intensity setting is adjusted to a first high-end intensity setting value and the low-end intensity setting is adjusted to a first low-end intensity setting value in the first operating mode, and the high-end intensity setting is adjusted to a second high-end intensity setting value and the low-end intensity setting is adjusted to a second low-end intensity setting value in the second operating mode.

In addition, the present invention provides a dimmer switch comprising a controllably conductive switching device and a user interface, wherein the improvement to the dimmer switch comprises a drive circuit responsive to the user interface to change the dimmer switch between first and second operating modes. The drive circuit is operable to adjust a high-end intensity setting of the dimmer switch to a first high-end intensity setting value and a low-end intensity setting of the dimmer switch to a first low-end intensity setting value in the first operating mode. The drive circuit is further operable to adjust the high-end intensity setting to a second high-end intensity setting value and the low-end intensity setting to a second low-end intensity setting value in the second operating mode.

According to another aspect of the present invention, a dimmer switch for controlling the intensity of a lighting load between a high-end intensity setting and a low-end intensity setting is operable to automatically adjust between first and second operating modes. The dimmer switch comprises a controllably conductive switching device adapted to be coupled in series electrical connection between an AC line voltage and the lighting load for controlling the amount of power delivered to the lighting load. The dimmer switch further comprises a controller operable to drive the controllably conductive switching device to change the controllably conductive switching device from a non-conductive state to a conductive state each half-cycle of the AC power source. The controller is operable to render the controllably conductive switching device conductive after a minimum off time following a zero-crossing of the AC line voltage, and to subsequently determine whether the controllably conductive switching device is conducting a load current to the lighting load. The controller is further operable to adjust the dimmer switch to one of the first operating mode and the second operating mode in response to whether the controllably conductive switching device is conducting current to the load, to adjust the high-end intensity setting to a first high-end intensity setting value and the low-end intensity setting to a first low-end intensity setting value in the first operating mode, and to adjust the high-end intensity setting to a second high-end intensity setting value and the low-end intensity setting to a second low-end intensity setting value in the second operating mode. Preferably, the second high-end intensity setting value is less than the first high-end intensity setting value, and the second low-end intensity setting value is greater than the first low-end intensity setting value.

According to another embodiment of the present invention, a dimmer switch comprises a first load terminal adapted to be coupled to an AC power source, a second load terminal adapted to be coupled to a lighting load, a controllably conductive switching device adapted to be coupled in series electrical connection between the first and second load terminals for controlling the amount of power delivered to the lighting load, a controller coupled to a control input of the controllably conductive switching device for controlling the controllably conductive switching device to be conductive for a conduction interval each half-cycle of the AC power source; and a sense circuit coupled such that the sense circuit is operable to sense an electrical characteristic of the second load terminal. The sense circuit is adapted to provide a control signal representative of the electrical characteristic to the controller, such that the controller is operable to change the dimmer switch between first and second operating modes in response to the control signal from the sense circuit. Accordingly, a high-end intensity setting of the dimmer switch is adjusted to a first high-end intensity setting value and a low-end intensity setting is adjusted to a first low-end intensity setting value in the first operating mode, while the high-end intensity setting is adjusted to a second high-end intensity setting value and the low-end intensity setting is adjusted to a second low-end intensity setting value in the second operating mode.

According to another embodiment of the present invention, a dimmer switch comprises a first load terminal adapted to be coupled to an AC power source, a second load terminal adapted to be coupled to a lighting load, a controllably conductive switching device, and a controller operable to automatically adjust the dimmer switch to one of a first operating mode and a second operating mode. The controllably conductive device is adapted to be coupled in series electrical connection between the first and second load terminals for controlling the amount of power delivered to the lighting load, and the controller is coupled to a control input of the controllably conductive switching device for controlling the controllably conductive switching device to be conductive for a conduction interval each half-cycle of the AC power source. A high-end intensity setting of the dimmer switch is adjusted to a first high-end intensity setting value and a low-end intensity setting is adjusted to a first low-end intensity setting value in the first operating mode, while the high-end intensity setting is adjusted to a second high-end intensity setting value and the low-end intensity setting is adjusted to a second low-end intensity setting value in the second operating mode.

The present invention further provides a method of controlling a dimmer switch adapted to be coupled between an AC power source and a lighting load, where the dimmer switch adapted to control the intensity of the lighting load between a high-end intensity setting and a low-end intensity setting. The method comprises the steps of: (1) conducting a load current from the AC power source to the lighting load for a conduction interval each half-cycle of the AC power source; (2) controlling the length of the conduction interval each half-cycle; (3) automatically changing the dimmer switch to one of first and second operating modes; (4) adjusting the high-end intensity setting to a first high-end intensity setting value and the low-end intensity setting to a first low-end intensity setting value when operating in the first operating mode; and (5) adjusting the high-end intensity setting to a second high-end intensity setting value and the low-end intensity setting to a second low-end intensity setting value when operating in the second operating mode. The second high-end intensity setting value is less than the first high-end intensity setting value, and the second low-end intensity setting value is greater than the first low-end intensity setting value.

In addition, the present invention provides, a dimmer switch comprising means for conducting a load current from an AC power source to a lighting load for a conduction interval each half-cycle of the AC power source, and means for controlling the length of the conduction interval each half-cycle, where the improvement to the dimmer switch comprises: means for automatically changing the dimmer switch to one of first and second operating modes, means for setting a high-end intensity setting to a first high-end intensity setting value and a low-end intensity setting to a first low-end intensity setting value when operating in the first operating mode, and means for adjusting the high-end intensity setting to a second high-end intensity setting value and the low-end intensity setting to a second low-end intensity setting value when operating in the second operating mode, the second high-end intensity setting value less than the first high-end intensity setting value, and the second low-end intensity setting value greater than the first low-end intensity setting value.

Other features and advantages of the present invention will become apparent from the following description of the invention that refers to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of a lighting system including a prior art dimmer circuit for controlling the intensity of an incandescent lamp;

FIG. 2A is a simplified diagram of a hot voltage received by the dimmer circuit ofFIG. 1 and a dimmed-hot voltage generated by the dimmer circuit to control the intensity of the incandescent lamp to a high-end intensity setting;

FIG. 2B is a simplified diagram of the hot voltage and the dimmed-hot voltage when the dimmer circuit ofFIG. 1 is controlling the intensity of the incandescent lamp to a low-end intensity setting;

FIG. 3 is a simplified block diagram of a lighting system including a prior art fluorescent Tu-Wire® dimmer circuit for driving a fluorescent load;

FIG. 4A is a simplified diagram of the hot voltage and the dimmed-hot voltage when the Tu-Wire® dimmer circuit ofFIG. 3 is controlling the intensity of the fluorescent lamp to a high-end intensity setting;

FIG. 4B is a simplified diagram of the hot voltage and the dimmed-hot voltage when the Tu-Wire® dimmer circuit ofFIG. 3 is controlling the intensity of the fluorescent lamp to a low-end intensity setting;

FIG. 5 is a simplified block diagram of the Tu-Wire® dimmer circuit ofFIG. 3 controlling a dimmable screw-in compact fluorescent lamp;

FIG. 6 is a simplified diagram of the hot voltage and the dimmed-hot voltage provided to the dimmable screw-in compact fluorescent lamp ofFIG. 5 when the Tu-Wire® dimmer circuit is attempting to control the intensity of the fluorescent lamp to the high-end intensity setting;

FIG. 7 is a simplified diagram of a dimmer switch for controlling the amount of power delivered to the dimmable screw-in compact fluorescent lamp according to a first embodiment of the present invention;

FIG. 8A is a simplified diagram of the hot voltage and the dimmed-hot voltage when the dimmer switch ofFIG. 7 is controlling the intensity of the dimmable screw-in compact fluorescent lamp to a high-end intensity setting;

FIG. 8B is a simplified diagram of the hot voltage and the dimmed-hot voltage when the dimmer switch ofFIG. 7 is controlling the intensity of the dimmable screw-in compact fluorescent lamp to a low-end intensity setting;

FIG. 9 is a perspective view of an example of the user interface of the dimmer switch ofFIG. 7 according to the first embodiment of the present invention;

FIG. 10 is a simplified schematic diagram of the dimmer switch ofFIG. 7 according to the first embodiment of the present invention;

FIGS. 11 and 12 are perspective views of a user interface of a dimmer switch according to a second embodiment of the present invention;

FIG. 13 is a simplified schematic diagram of the dimmer switch ofFIGS. 11 & 12;

FIG. 14 is a front view of a user interface of a “smart” dimmer switch according to a third embodiment of the present invention;

FIG. 15 is a simplified block diagram of the dimmer switch ofFIG. 14;

FIG. 16 is a simplified flowchart of a control procedure executed periodically by a controller of the dimmer circuit ofFIG. 15;

FIG. 17 is a simplified flowchart of a power-up procedure executed by the controller of the dimmer switch ofFIG. 15;

FIG. 18 is a simplified flowchart of an advanced programming mode routine executed by the controller of the dimmer switch ofFIG. 15;

FIG. 19 is a simplified block diagram of a smart dimmer switch according to a fourth embodiment of the present invention;

FIG. 20 is a simplified flowchart of a power-up procedure executed by a controller of the dimmer switch ofFIG. 19;

FIG. 21 is a simplified flowchart of an operating mode update routine executed by the controller of the dimmer switch ofFIG. 19 to automatically detect the type of lamp connected to the dimmer switch; and

FIG. 22 is a simplified flowchart of a control procedure executed periodically by the controller of the dimmer switch ofFIG. 19.

DETAILED DESCRIPTION OF THE INVENTION

The foregoing summary, as well as the following detailed description of the preferred embodiments, is better understood when read in conjunction with the appended drawings. For the purposes of illustrating the invention, there is shown in the drawings an embodiment that is presently preferred, in which like numerals represent similar parts throughout the several views of the drawings, it being understood, however, that the invention is not limited to the specific methods and instrumentalities disclosed.

FIG. 7 is a simplified diagram of a dimmer switch100 (i.e., a dimmer circuit) for controlling the amount of power delivered to the dimmable screw-incompact fluorescent lamp34 according to a first embodiment of the present invention. Particularly, thedimmer switch100 of the present invention is able to control the intensity of the dimmable screw-incompact fluorescent lamp34 to the high-end intensity setting while avoiding multiple firings. It was discovered that reducing the conduction interval T_CONby approximately 0.6 msec near the high-end intensity setting of thedimmer switch100 did not visibly change the light output of thefluorescent lamp38, but eliminated the problem of multiple firings. When controlling an incandescent lamp (as with the prior art dimmer circuit10) or a two-wire ballast (as with the prior art dimmer circuit20), it is desirable to maximize the conduction interval T_CONto provide the maximum possible light output of the connected lighting load at the high-end intensity setting. In contrast, thedimmer switch100 of the present invention has a conduction interval T_CONat the high-end intensity setting that is shorter in length than the maximum conduction intervals of the prior artdimmer circuits10,20.

In order to minimize the size and cost of the ballast circuit, the ballast circuit of a typical dimmable screw-in compact fluorescent lamp does not have an active front-end (i.e., a boost converter). Instead, the ballast circuit of a typical dimmable screw-in compact fluorescent lamp simply comprises a rectifier (e.g., a full-wave rectifier diode bridge) having an AC input coupled to theAC power supply12 and a DC output coupled to a bus capacitor. When the prior art Tu-Wire®dimmer circuit20 attempts to control the dimmable screw-incompact fluorescent lamp34 to the high-end intensity setting, the triac is fired before the instantaneous magnitude of the AC line voltage rises above the voltage across the bus capacitor (plus the voltage drop of the rectifier) of theballast circuit36. Accordingly, the current drawn by theballast circuit36 does not exceed the latching current (i.e., 15 mA) of the triac and the triac fires multiple times (as shown inFIG. 6).

It was determined that the off time T_OFFof the triac at the beginning of each half-cycle could be increased (i.e., the conduction interval T_CONcould be reduced), such that the triac is prevented from being fired until after the instantaneous magnitude of the AC line voltage exceeds the voltage across the bus capacitor. Specifically, the conduction interval T_CONcan be reduced to less than approximately 75% of each half-cycle without reducing the maximum light output of the dimmable screw-incompact fluorescent lamp34.

FIG. 8A is a simplified diagram of the hot voltage V_Hand the dimmed-hot voltage V_DHprovided to the dimmable screw-incompact fluorescent lamp34 when thedimmer switch100 is controlling the intensity of the dimmable screw-in compact fluorescent lamp to the high-end intensity setting.FIG. 8B is a simplified diagram of the hot voltage V_Hand the dimmed-hot voltage V_DHwhen thedimmer switch100 is controlling the intensity of the dimmable screw-incompact fluorescent lamp34 to the low-end intensity setting. As shown inFIG. 8A, the high-end intensity setting has been reduced, such that the off time T_OFFis greater than approximately 2.2 msec, and is preferably 2.5 msec. The magnitude of the resulting dimmed-hot voltage V_DHis approximately 108 to 114 V_RMS. Accordingly, thedimmer switch100 conducts current to thefluorescent lamp34 for the conduction interval T_CONfor less than approximately 75% of each half-cycle, and preferably less than approximately 70% of each half-cycle, at the high-end intensity setting. The low-end intensity setting as shown inFIG. 8B remains the same as that of the prior art dimmer circuit20 (i.e., the off time T_OFFis approximately 5.6 msec).

FIG. 9 is a perspective view of an example of the user interface of thedimmer switch100. Thedimmer switch100 includes arocker switch102 and an intensity adjustment actuator104 (i.e., a slider actuator). Therocker switch102 allows for turning on and off the screw-incompact fluorescent lamp34. Theintensity adjustment actuator104 allows for adjustment of the lighting intensity of thefluorescent lamp34 from the low-end intensity setting to the high-end intensity setting. Thedimmer switch100 also includes abezel105 attached to afront surface106 of a mountingyoke108 and a printed circuit board (not shown) mounted inside thedimmer switch100. Thebezel105 is adapted to be received in an opening of a faceplate (not shown).

FIG. 10 is a simplified schematic diagram of thedimmer switch100 according to the present invention. Thedimmer switch100 includes a controllably conductive switching device coupled in series between the hot terminal and the dimmed-hot terminal for controlling the amount of power delivered to the screw-incompact fluorescent lamp34. Specifically, as shown inFIG. 10, the controllably conductive switching device of thedimmer switch100 is implemented as a triac Q₁. The triac Q₁includes a control input (i.e., a gate) for rendering the triac conductive after the off time each half-cycle of theAC power source12. The triac Q₁has a low holding current rating, for example, less than approximately 35 mA, but preferably approximately 15 mA.

Thedimmer switch100 also comprises a mechanical switch S_M, afilter circuit110 and a phase-cut AC drive circuit including avoltage compensation circuit120, atiming circuit130, and atrigger circuit140. Thevoltage compensation circuit120, thetiming circuit130, and thetrigger circuit140 operate to render the triac conductive for the conduction interval T_CONeach half-cycle of theAC power source12. The mechanical switch S_Mcomprises, for example, a single-pole single-throw (SPST) switch and is coupled in series electrical connection between theAC power source12 and the remainder of the circuitry of thedimmer switch100. The mechanical switch S_Mis mechanically coupled to therocker switch102, such that a user of thedimmer switch100 is able to actuate the rocker switch to open and close the mechanical switch and to thus control the screw-incompact fluorescent lamp34 to be off and on, respectively.

Thefilter circuit110 includes a resistor R_F(e.g., having a resistance of 220Ω) and a capacitor C_F(e.g., having a capacitance of 0.047 μF) coupled in series between the hot terminal H and the dimmed-hot terminal DH. Thefilter circuit110 also includes an inductor L_Fthat is coupled in series with the triac Q₁and preferably has an inductance of 10 to 50 μH. The main purpose of thefilter circuit110 is to reduce the EMI noise present at the hot terminal H and the dimmed-hot terminal DH. The EMI noise is generated by the switching of the triac Q₁each half-cycle of theAC power source12. However, the resistor R_Fand the capacitor C_Falso function to minimize ringing of the dimmed-hot voltage V_DHwhen the triac Q₁changes from being non-conductive to conductive each half-cycle.

The series combination of thevoltage compensation circuit120 and thetiming circuit130 is coupled in parallel with the triac Q₁. Thevoltage compensation circuit120 compensates for voltage fluctuations of the AC source voltage of theAC power source12, such that the length of the conduction interval of the triac Q₁does not undesirably change from one half-cycle to the next, as will be described in greater detail below. Thetiming circuit130 has an output coupled to thetrigger circuit140 for providing a timing voltage representative of a desired light intensity of the screw-incompact fluorescent lamp34. Thetrigger circuit140 preferably comprises a diac D_TRIG(e.g., part number DB3 manufactured by ST Microelectronics), which has a break-over voltage of approximately 30 V and is coupled in series between the output of thetiming circuit130 and the gate of the triac Q₁.

Thetiming circuit130 includes a firing capacitor C_FIREand a potentiometer R_POTthat is mechanically coupled to theintensity adjustment actuator104. The firing capacitor C_FIREpreferably has a capacitance of 0.047 μF and charges each half-cycle through the potentiometer R_POT. The timing voltage is produced across the firing capacitor C_FIREand increases in magnitude with respect to time as the firing capacitor charges. The potentiometer R_POTprovides a variable resistance, such that the user may adjust the potentiometer to adjust the rate at which the firing capacitor C_FIREcharges to thus set the desired intensity of thefluorescent lamp34. During each half-cycle, the timing voltage increases in magnitude at a rate dependent upon the present resistance of the potentiometer R_POTand thus the desired intensity of the lamp. When the timing voltage exceeds the break-over voltage of the diac D_TRIG, the voltage across the diac quickly decreases in magnitude to a break-back voltage. The change in voltage across the diac D_TRIGcauses the diac to conduct a gate current through the gate of the triac Q₁, thus rendering the triac conductive.

The potentiometer R_POTof thetiming circuit130 has two main terminals and a wiper terminal coupled to one of the main terminals. The potentiometer R_POTpreferably has a maximum resistance of 300 kΩ. The wiper of the potentiometer R_POTis moveable, so that the resistance between one of the two main terminals of the potentiometer is variable from 0Ω to 300 kΩ. A calibration resistor R_CALis coupled between the two main terminals of the potentiometer R_POTand functions to establish the low-end intensity setting of thedimmer switch100. The calibration resistor R_CALpreferably has a resistance of approximately 110 kΩ, such that the resistance between the two main terminals of the potentiometer is scaled to range from 0Ω to about 80 kΩ.

Thetiming circuit130 further comprises a high-end intensity regulation circuit, e.g., a high-end limiting resistor R_HEcoupled in series with the parallel combination of the potentiometer R_POTand the calibration resistor R_CAL. The firing capacitor C_FIREis operable to charge through the potentiometer R_POT, the calibration resistor R_CAL, and the high-end resistor R_HE. The junction of the firing capacitor C_FIREand the high-end resistor R_HEis the output to thetrigger circuit140. The high-end resistor R_HEhas a resistance greater than approximately 22 kΩ, such that the off time T_OFFof the triac Q₁is at least 2.2 msec, and the conduction interval T_CONis limited to approximately 75% of each half-cycle. This increase in resistance of the high-end resistor R_HEunexpectedly makes it possible to achieve proper dimming of a dimmable screw-in compact fluorescent lamp, which could not be acceptably dimmed by the prior artdimmer circuits10,20. Preferably, the resistance of the high-end resistor R_HEis 44 kΩ, such that the off time T_OFFof the triac Q₁is approximately 2.5 msec, and the conduction interval T_CONis limited to approximately 70% of each half-cycle.

Thevoltage compensation circuit120 includes a resistor R_VC(e.g., having a resistance of 27 kΩ) and two series-coupled diacs D_VC1, D_VC2(e.g., each having a break-over voltage of 30 V). Since the diacs D_VC1, D_VC2have negative impedance transfer functions, the current through the diacs decreases as the voltage across the diacs increases. Thus, when the AC source voltage of the AC power source12 (and thus, the voltage across the voltage compensation circuit120) decreases, the current through the resistor R_VCand the diacs D_VC1, D_VC2decreases and the voltage across the diacs increases. As a result, the current flowing through the potentiometer R_POT, the calibration resistor R_CAL, and the high-end resistor R_HE, and into the firing capacitor C_FIREincreases, thus causing the timing voltage to exceed the break-over voltage of the diac D_TRIGmore quickly during the present half-cycle. The conduction interval T_CONis thus longer for the present half-cycle, thereby compensating for the decreased output voltage of theAC power source12 and maintaining the light output of thelamp34 substantially constant. A similar situation occurs when the AC source voltage of theAC power source12 increases and the conduction interval T_CONis accordingly controlled to be shorter.

Thevoltage compensation circuit120 also operates to allow theballast circuit36 to strike the screw-incompact fluorescent lamp34 if the switch S_Mis closed (i.e., changes from open to closed) when thedimmer switch100 is controlling the lamp to a light intensity near the low-end intensity setting. This eliminates the occurrence of the lamp “popping on” if the potentiometer R_POTis adjusted to increase the intensity of the lamp from the low-end intensity setting to a point at which the lamp can strike.

Therefore, thedimmer switch100 according to the present invention provides smooth dimming of a dimmable screw-in compact fluorescent lamp. Since the high-end intensity setting is significantly lower, and the off time T_OFFis greater, than in the prior artdimmer circuits10,20, thedimmer switch100 prevents unwanted multiple firings of the controllably conductive switching device Q₁, thus avoiding flickering of the fluorescent lamp, audible noise in the lamp, increased EMI noise, and unneeded stress on the components of the dimmer switch and the ballast circuit of the lamp.

FIGS. 11 and 12 are perspective views of a user interface of adimmer switch200 according to a second embodiment of the present invention. Thedimmer switch200 includes a user-accessible operatingmode adjustment actuator250 that allows a user to change thedimmer switch200 between an incandescent load operating mode and a screw-in compact fluorescent load operating mode. When the operatingmode adjustment actuator250 is in a first position, thedimmer switch200 operates in the incandescent load operating mode. Accordingly, the high-end intensity setting of the dimmer switch is adjusted to a first high-end intensity setting value and the low-end intensity setting is adjusted to a first low-end intensity setting value. When the operatingmode adjustment actuator250 is in a second position, thedimmer switch100 operates in the screw-in compact fluorescent load operating mode, such that the high-end intensity setting is adjusted to a second high-end intensity setting value and the low-end intensity setting is adjusted to a second low-end intensity setting value. Preferably, the second high-end intensity setting value is lower than the first high-end intensity setting value, and the second low-end intensity setting value is higher than the first low-end intensity setting value.

Referring toFIG. 12, the operatingmode adjustment actuator250 is coupled to amechanical switch260 mounted on a printedcircuit board262 via acoupling member264. Themechanical switch260 includes anactuation knob266, which is received in a notch in thecoupling member264. The operatingmode adjustment actuator250 is provided in anopening268 between thebezel105 and a front surface206 of a mounting yoke208, such that the user is able to change the operating mode from the user interface of thedimmer switch200. The yoke208 includes engraving (i.e., the words “INCANDESCENT” and “FLUORESCENT”) near the operatingmode adjustment actuator250 to specify which of the operating modes thedimmer switch200 is selected (depending upon the position of the operating mode adjustment actuator). Preferably, the operatingmode adjustment actuator250 is located such that the adjustment actuator cannot be seen when the faceplate is mounted to thedimmer switch200, but can be accessed when the faceplate is removed.

FIG. 13 is a simplified schematic diagram of thedimmer switch200 coupled to alighting load202 that may comprise an incandescent lamp or a dimmable screw-in compact fluorescent lamp. Themechanical switch260 that is coupled to theload adjustment actuator250 preferably comprises a single-pole double-throw (SPDT) switch and is included as part of atiming circuit230. Thetiming circuit230 includes two calibration resistors R_CAL1, R_CAL2that are coupled in series and preferably each have resistances of 95 kΩ and 30 kΩ, respectively. The series combination of the calibration resistors R_CAL1, R_CAL2is coupled in parallel with the potentiometer R_POT(i.e., in place of the calibration resistor R_CALof thedimmer switch100 of the first embodiment). Thetiming circuit230 also includes two high-end resistors R_HE1, R_HE2, which are coupled in series and preferably have resistances of 22 kΩ and 5.6 kΩ, respectively. The series combination of the high-end resistors R_HE1, R_HE2is coupled between the potentiometer R_POTand the trigger circuit140 (i.e., in place of the high-end resistor R_HEof thedimmer switch100 of the first embodiment).

Themechanical switch260 has a moveable contact and two fixed contacts. The moveable contact is coupled to the junction of the potentiometer R_POT, the second calibration resistor R_CAL2, and the first high-end resistor R_HE1. The first fixed contact is coupled to the junction of the two calibration resistors R_CAL1, R_CAL2, while the second fixed contact is coupled to the junction of the two high-end resistors R_HE1, R_HE2. When the operatingmode adjustment actuator250 is in the first position and themechanical switch260 is in position A (as shown inFIG. 13), thedimmer switch200 is in the incandescent operating mode. At this time, the first high-end resistor R_HE1is shorted out and only the second high-end resistor R_HE2(i.e., only 5.6 kΩ) is coupled in series between the potentiometer R_POTand thetrigger circuit140. Accordingly, the high-end intensity setting of thedimmer switch200 is adjusted to the first high-end intensity setting value (e.g., the off time T_OFFof the triac Q₁is approximately 1.4 msec). Further, the series combination of the calibration resistors R_CAL1, R_CAL2(i.e., 150 kΩ) is coupled in parallel with the potentiometer R_POT, such that the low-end intensity setting of thedimmer switch200 is adjusted to the first low-end intensity setting value (e.g., the off time T_OFFof the triac Q₁is approximately 6.8 msec).

When theload adjustment actuator250 is in the second position and themechanical switch260 is in position B, thedimmer switch200 is in the screw-in compact fluorescent operating mode. The second calibration resistor R_CAL2is shorted out and only the first calibration resistor R_CAL1(i.e., only 75 kΩ) is coupled in parallel with the potentiometer R_POT, such that the low-end intensity setting of thedimmer switch200 is adjusted to the second low-end intensity setting value (e.g., the off time T_OFFof the triac Q₁is approximately 5.6 msec). The series-combination of the two high-end resistors R_HE1, R_HE2(i.e., 27.6 kΩ) is coupled in series between the potentiometer R_POTand thetrigger circuit140, and the high-end intensity setting of thedimmer switch200 is adjusted to the second high-end intensity setting value (e.g., the off time T_OFFof the triac Q₁is approximately 2.5 msec).

The conduction interval T_CONat the high-end intensity setting in the screw-in compact fluorescent operating mode is preferably shorter in length than the conduction interval T_CONat the high-end intensity setting in the incandescent operating mode. The conduction interval T_CONat the low-end intensity setting in the screw-in compact fluorescent operating mode is preferably greater in length than the conduction interval T_CONat the low-end intensity setting in the incandescent operating mode. Therefore, the dynamic range of the dimmer switch200 (i.e., the range of the value of the conductive interval T_CONat the high-end intensity setting to the value of the conduction interval T_CONat the low-end intensity) decreases when the dimmer switch changes from the incandescent operating mode to the screw-in compact fluorescent operating mode.

FIG. 14 is a front view of auser interface301 of a “smart”dimmer switch300 according to a third embodiment of the present invention. Thedimmer switch300 comprises acontrol actuator302 and an intensity adjustment actuator304 (i.e., a rocker switch). An actuation of thecontrol actuator302 causes thedimmer switch300 to toggle thelighting load202 between on and off. An actuation of theupper portion304A of theintensity adjustment actuator304 raises the light intensity of thelighting load202, while an actuation of thelower portion304B of the intensity adjustment actuator lowers the light intensity. Thecontrol actuator302 and theintensity adjustment actuator304 are provided on the front surface of abezel305, which is received in the opening of afaceplate306. An air-gap switch actuator309 actuates an internal mechanical switch S_AG(FIG. 15) to provide an actual air-gap break between theAC power source12 and thelighting load202.

Thedimmer switch300 also includes a plurality ofvisual indicators308, e.g., light-emitting diodes (LEDs) that are arranged in a linear array on thebezel305. Thevisual indicators308 are illuminated to represent the present light intensity level of thelighting load202. The light intensity level is typically expressed as a percentage of full intensity, i.e., the light intensity level may range from 1% to substantially 100%. When thedimmer switch300 is controlling the intensity of thelighting load202 to the low-end intensity setting, the lowestvisual indicator308 is illuminated. When thedimmer switch300 is controlling the intensity of thelighting load202 to the high-end intensity setting, the highestvisual indicator308 is illuminated.

According to the present invention, a user may change thedimmer switch300 between the incandescent operating mode and the screw-in compact fluorescent operating mode from theuser interface301 of the dimmer switch by using, for example, an advanced programming mode. The advanced programming mode may be entered, for example, by holding thecontrol actuator302, while cycling power to thedimmer switch300, e.g., by actuating the air-gap switch actuator309. The advanced programming mode also allows the user to modify other advanced programming features of thedimmer switch300, such as a protected preset or a fade rate. A dimmer switch having an advanced programming mode is described in greater detail in commonly-assigned U.S. Pat. No. 7,190,125, issued Mar. 13, 2007, entitled PROGRAMMABLE WALLBOX DIMMER, the entire disclosure of which is hereby incorporated by reference.

Often, dimmable screw-in compact fluorescent lamps from different manufacturers may be controlled to different low-end intensity settings. Therefore, thedimmer switch300 of the present invention allows the user to adjust the minimum low-end intensity setting of thedimmer switch300 to match the minimum low-end intensity setting of a connected dimmable screw-in compact fluorescent lamp, based on the manufacturer of the lamp, in order to provide the maximum range of dimming of the lamp. Preferably, the minimum low-end intensity setting of thedimmer switch300 is adjusted using the advanced programming mode so as to ensure that the low-end intensity setting of thedimmer switch300 is adjusted to the appropriate level for the particular connected dimmable screw-in compact fluorescent lamp.

FIG. 15 is a simplified block diagram of the “smart”dimmer switch300. Thedimmer switch300 includes a controllablyconductive switching device312 coupled in series electrical connection between the hot terminal H and the dimmed hot terminal DH for controlling the intensity of thelighting load202. The controllablyconductive switching device312 may be implemented as any suitable switching device, such as, for example, a triac or two SCRs. The mechanical air-gap switch S_AGis coupled in series with the controllablyconductive switching device312 to provide an actual air-gap break between theAC power source12 and thelighting load202 in response to an actuation of the air-gap switch actuator309. Thedimmer switch300 further comprises a neutral terminal N adapted to coupled to the neutral side of theAC power source12, and afilter circuit310, including a resistor R_F, a capacitor C_F, and an inductor L_F, for minimizing the amount of EMI noise at the hot terminal H and the dimmed-hot terminal DH.

Acontroller316 is coupled to a control input of the controllablyconductive switching device312 via agate drive circuit314 for selectively controlling the controllablyconductive switching device312 to be conductive and non-conductive. Specifically, thecontroller316 drives the controllablyconductive switching device312 to render the controllably conductive switching device conductive for a portion of each half-cycle of the AC line voltage of theAC power source12. As defined herein, “driving” refers to applying a control signal to a gate of a thyristor, such as a triac or a silicon-controller rectifier (SCR), to enable a gate current to flow in the gate of the thyristor, such that the thyristor is conductive. When the thyristor is “conductive”, the gate current flows through the gate of the thyristor and the thyristor is operable to conduct a load current. The load current is defined as a current having a magnitude greater than the latching current of the thyristor. If the current through the main load terminals of the thyristor exceeds the latching current of the thyristor (while the thyristor is being driven), the thyristor then conducts the load current and the thyristor is defined to be in “conduction”.

Thecontroller316 may be any suitable controller, such as a microcontroller, a microprocessor, a programmable logic device (PLD), or an application specific integrated circuit (ASIC). Thecontroller316 receives inputs from thecontrol actuator302 and theintensity adjustment actuator304 of theuser interface301, and outputs intensity information to the user interface, such that thevisual indicators308 are operable to display the intensity of thelighting load202. Thecontroller316 determines a desired intensity to which to control thelighting load202 in response to thecontrol actuator302 and theintensity adjustment actuator304. When in the screw-in compact fluorescent lamp operating mode, thecontroller316 is operable to limit the high-end intensity setting of thedimmer circuit300, such that the length of the conduction interval T_CONdoes not exceed at least 75% of each half-cycle, and preferably does not exceed 70% of each half-cycle.

Thecontroller316 is coupled to amemory318 for storage of the desired intensity of thelighting load202, the operating mode of thedimmer switch300, and other information regarding a connected dimmable screw-in compact fluorescent lamp, such as, for example, the manufacturer of the lamp. Alternatively, thememory318 could be integral to thecontroller316. Apower supply320 is coupled between the hot terminal H and the neutral terminal N, such that the power supply does not draw current through thelighting load202. Thepower supply320 generates a direct-current (DC) voltage V_CC, e.g., 5 V_DC, for powering thecontroller316 and other low-voltage circuitry of thedimmer circuit300.

A zero-crossingdetector322 is coupled between the hot terminal H and the neutral terminal N for determining the zero-crossing points of the AC source voltage provided by theAC power supply12. A zero-crossing is defined as the time at which the AC supply voltage transitions from positive to negative polarity, or from negative to positive polarity, at the beginning of each half-cycle. The zero-crossing information is provided as an input to thecontroller316. Thecontroller316 generates the gate control signals to render the controllablyconductive switching device312 conductive and non-conductive at predetermined times relative to the zero-crossing points of the AC source voltage.

Alternatively, if thepower supply320 is able to draw an adequate amount of current through thelighting load202 to appropriately generate the DC voltage V_CCwithout illuminating thelighting load202, thefilter circuit310, thepower supply320, and the zero-crossingdetector322 could be coupled across the controllablyconductive switching device312 and thedimmer switch200 would not require the neutral terminal N for connection to the neutral side of theAC power source12.

FIG. 16 is a simplified flowchart of acontrol procedure330 executed periodically by thecontroller316, e.g., once every half-cycle of theAC power source12 when the zero-crossingdetector322 detects a zero-crossing atstep332. If thecontroller316 determines that thecontrol actuator302 has been actuated atstep334, a determination is made atstep336 as to whether thelighting load202 is presently on. If so, thecontroller316 stores the light intensity as off (i.e., 0%) in thememory318 atstep338, and controls the controllablyconductive switching device312 appropriately at step340 (i.e., does not render the controllably conductive switching device conductive during the present half-cycle). If thelighting load202 is off atstep336, thecontroller316 loads the previously-stored light intensity from thememory318 atstep342, and controls the controllably conductive switching device to turn on to the appropriate light intensity at step340 (i.e., renders the controllably conductive switching device conductive at the appropriate time during the present half-cycle).

If thecontroller316 determines that thecontrol actuator302 has not been actuated atstep334, a determination is made as to whether theupper portion304A of theintensity adjustment actuator304 has been actuated atstep344. If theupper portion304A has been actuated atstep344, thelighting load202 is on atstep346, and the light intensity is not at the high-end intensity setting atstep348, thecontroller316 increases the light intensity by a predetermined increment (e.g., 1%) atstep350, and controls the controllably conductive switching device atstep340. If the intensity of thelighting load202 is at the high-end intensity setting atstep348, thecontroller316 does not change the light intensity, such that the light intensity is limited to the high-end intensity setting. If theupper portion304A is being actuated atstep344 and thelighting load202 is not on atstep346, the intensity of thelighting load202 is adjusted to the low-end intensity setting atstep352, and the controllably conductive switching device is controlled appropriately at step340 (i.e., the lighting load is turned on to the low-end intensity setting).

If theupper portion304A of theintensity adjustment actuator304 has not been actuated atstep344, but thelower portion304B has been actuated atstep354, a determination is made atstep356 as to whether thelighting load202 is on. If thelighting load202 is on atstep356 and the light intensity is not at the low-end intensity setting atstep358, the light intensity is decreased by a predetermined increment (e.g., 1%) atstep360. If the light intensity is at the low-end intensity setting atstep358, thecontroller316 does not change the light intensity, such that the light intensity remains at the low-end intensity setting. If thelighting load202 is not on atstep356, the light intensity is not changed (i.e., thelighting load202 remains off) and the controllablyconductive switching device312 is not rendered conductive atstep340.

If thecontrol actuator302 has not been actuated atstep334, theupper portion304A of theintensity adjustment actuator304 has not been actuated atstep344, and thelower portion304B of the intensity adjustment actuator has not been actuated atstep354, the controllably conductive switching device is controlled appropriate atstep340. After the controllably conductive switching device is appropriately controlled atstep340 each half-cycle, thecontrol procedure330 exits. Thecontrol procedure330 is executed by thecontroller316 once again at the next zero-crossing of the AC line voltage.

FIG. 17 is a simplified flowchart of a power-upprocedure370 that enables thecontroller316 to modify the operating mode of thedimmer switch300 using an advanced programming mode routine380 (FIG. 18). The power-upprocedure370 is executed by thecontroller316 when the controller is first powered up atstep372, for example, in response to the user cycling power to thedimmer switch300 by actuating the air-gap switch actuator309. First, thecontroller316 reads thememory318 atstep374 to determine the present intensity of thelighting load202, the operating mode of thedimmer switch300, and the manufacturer of a connected dimmable screw-in compact fluorescent lamp. If thecontrol actuator302 is not being pressed atstep375 when thecontroller316 powers up, the power-upprocedure370 simply exits and thedimmer switch300 enters normal operation.

However, if thecontrol actuator302 is being pressed atstep375 when thecontroller316 powers up, theprocedure370 loops until thecontrol actuator302 is released atstep376, or a time period T_APM(e.g., approximately five seconds since thecontroller316 started the power-up procedure370) expires atstep378. If thecontrol actuator302 is released atstep376 before the end of the time period T_APM, the power-upprocedure370 simply exits. On the other hand, if thecontrol actuator302 is held for the length of the time period T_APMatstep378, thecontroller316 executes the advancedprogramming mode routine380 and then exits to normal operation.

FIG. 18 is a simplified flowchart of the advancedprogramming mode routine380. If the user makes a change to the operating mode of thedimmer switch300 atstep382, a determination is made as to whether the mode is being changed to the screw-in compact fluorescent operating mode atstep384, or to the incandescent operating mode atstep385. If the operating mode is being changed to the incandescent operating mode atstep385, thecontroller316 adjusts the high-end intensity setting to a first high-end (HE) intensity value (e.g., the off time T_OFFof the controllablyconductive switching device312 is approximately 1.4 msec) and adjusts the low-end intensity setting to a first low-end (LE) intensity value (e.g., the off time T_OFFof the controllablyconductive switching device312 is approximately 6.8 msec) atstep386.

If the operating mode is being changed to the screw-in fluorescent operating mode atstep384, thecontroller316 adjusts the high-end intensity setting to a second high-end intensity setting value (e.g., the off time T_OFFof the controllablyconductive switching device312 is approximately 2.5 msec) atstep388, and then determines the manufacturer of the connected dimmable screw-in compact fluorescent lamp (as stored in the memory318) in order to adjust the low-end intensity setting to the appropriate intensity value. Specifically, if the fluorescent lamp is a Philips® dimmable screw-in compact fluorescent lamp atstep390, thecontroller316 adjusts the low-end intensity setting to a second low-end intensity setting value (e.g., the off time T_OFFof the controllablyconductive switching device312 is approximately 5.6 msec) atstep392. Alternatively, if thecontroller316 determines atstep394 that the dimmable screw-in compact fluorescent lamp is manufactured by General Electric (GE), the controller adjusts the low-end intensity setting to a third low-end intensity setting value (e.g., the off time T_OFFof the controllablyconductive switching device312 is approximately 6.2 msec) atstep395. Additionally, thecontroller316 could allow the user to select from other manufacturers of dimmable screw-in compact fluorescent lamps.

If the user is not changing the operating mode of thedimmer switch300 atstep382, but the user is changing the manufacturer of the screw-in compact fluorescent lamp atstep396, thecontroller316 adjusts the low-end intensity setting of the dimmer switch atsteps392 and395 in response to the manufacturer determined atsteps390 and394, respectively. If the user chooses to exit the advanced programming mode atstep398, or if a timeout (e.g., five seconds since the last actuation of either of thecontrol actuator302 and the intensity adjustment actuator304) expires atstep399, the advancedprogramming mode routine380 exits. Otherwise, the advancedprogramming mode routine380 loops to allow the user to change the operating mode or the manufacturer of the connected dimmable screw-in compact fluorescent lamp once again.

FIG. 19 is a simplified block diagram of asmart dimmer switch400 according to a fourth embodiment of the present invention. Thesmart dimmer400 is operable to automatically determine the type of lamp (e.g., an incandescent lamp or a dimmable screw-in compact fluorescent lamp) is coupled to the dimmer switch, and to accordingly change between the incandescent operating mode and the screw-in compact fluorescent operating mode. Preferably, the controllablyconductive switching device312 comprises a triac, and acontroller416 is operable to detect the occurrence of multiple firings of the triac (as shown inFIG. 6) to determine that a dimmable screw-in compact fluorescent lamp is connected to thedimmer switch400. Specifically, upon first powering up, thecontroller416 is operable to render the triac conductive after the power supply charging time T_CHGfollowing the next zero-crossing of the AC line voltage. Thecontroller416 is operable to determine whether the triac latches and becomes conductive in response to the voltage sensed across the triac by the voltage detectcircuit424.

Thedimmer switch400 comprises a voltage detect circuit424 (i.e., a sensing circuit) that is coupled across the controllablyconductive switching device312 and provides a control signal representative of the magnitude of the voltage across the controllably conductive switching device to thecontroller416. Preferably, the voltage detectcircuit424 simply compares the voltage across the triac to a predetermined voltage threshold (e.g., approximately 2 volts). If the voltage across the triac is less than the predetermined voltage threshold, the triac has latched and is conducting the load current to thelighting load202. This indicates that thelighting load202 is an incandescent lamp. At this time, the voltage detectcircuit424 preferably provides the control signal at a logic high level (e.g., approximately the DC voltage generated by thepower supply320, i.e., 5 V_DC). When the voltage across the triac is greater than the predetermined voltage threshold, the triac has not latched, and the triac is non-conductive. This indicates that thelighting load202 is a dimmable screw-in compact fluorescent lamp. Accordingly, the voltage detectcircuit424 preferably drives the control signal to a logic low level (e.g., approximately circuit common).

Thedimmer switch400 of the present invention is not limited to comprising a voltage detect circuit coupled across the controllablyconductive switching device312 for determining whether the controllably conductive switching device is conducting the load current. Alternatively, the voltage detectcircuit424 may comprise any type of sensing circuit capable of sensing an electrical characteristic of the load terminal connected to the lighting load202 (i.e., the dimmed-hot terminal DH), wherein the electrical characteristic is representative of the type of lighting load connected to thedimmer switch400. For example, the electrical characteristic may comprise the load current or the voltage of at the dimmed-hot terminal DH (referenced to the hot terminal H).

FIG. 20 is a simplified flowchart of a power-upprocedure440 executed by thecontroller416 of thedimmer switch400. The power-upprocedure440 allows for manual adjustment of the operating mode of thedimmer switch400, but also provides for automatic adjustment of the operating mode. Specifically, if thelighting load202 should be on when thecontroller416 is powered up (as determined from the memory318), thecontroller416 monitors the voltage across the controllablyconductive switching device312 and adjusts the operating mode during the power-upprocedure440. However, if thelighting load202 should be off when thecontroller416 is powered up, the controller waits until the lamp is next turned on to adjust the operating mode. Thecontroller416 uses a flag CHK_LOAD to signal that the operating mode should be adjusted (if needed) when thelighting load202 is next turned on. The flag CHK_LOAD is cleared atstep442 at the beginning of the power-upprocedure440.

If thecontrol actuator302 is pressed atstep375 when thecontroller416 first powers up atstep372, but is not released atstep376 before the end of the time period T_APMatstep378, thecontroller416 executes the advancedprogramming mode procedure380 to allow the user to manually change the operating mode of thedimmer switch400 and the manufacturer of a connected dimmable screw-in compact fluorescent lamp (as was described with reference toFIG. 18).

However, if thecontrol actuator302 is not pressed atstep375 or the actuator is released before the end of the time period T_APMatstep378, a determination is made atstep444 as to whether thelighting load202 is on. If so, thecontroller416 executes an operating mode update routine450 (FIG. 21) to automatically detect the type of lamp connected to thedimmer switch400. If thelighting load202 is not on atstep444, the flag CHK_LOAD is set atstep446, such that thecontroller416 will execute the operatingmode update routine450 the next time thelighting load202 is turned on.

FIG. 21 is a simplified flowchart of the operatingmode update routine450 executed by thecontroller416 to automatically detect the type of lamp connected to thedimmer switch400. First, thecontroller416 waits for the next zero-crossing atstep452 and then waits for a first time period T_w1at step454, before rendering the controllablyconductive switching device312 conductive atstep455. Next, thecontroller416 waits atstep456 for a second time period T_W2, i.e., an appropriate amount of time for the controllablyconductive switching device312 to latch (e.g., 400 μsec after rendering the controllably conductive switching device conductive). At the end of the time period T_W2atstep458, thecontroller416 reads the input provided by the voltage detectcircuit424. If the control signal provided by the voltage detectcircuit424 signals that the voltage across the controllablyconductive switching device312 is less than the predetermined voltage threshold at step460 (i.e., the controllably conductive has latched and is conducting the load current to the lighting load202), thecontroller416 determines that thelighting load202 is not a dimmable screw-in compact fluorescent lamp. Accordingly, thecontroller416 adjusts the operating mode of thedimmer switch400 to the incandescent operating mode by adjusting the high-end intensity setting to the first high-end intensity setting value and the low-end intensity setting to the first low-end intensity setting value atstep462.

If the control signal from the voltage detectcircuit424 indicates that the voltage across the controllablyconductive switching device312 is greater than the predetermined voltage threshold at step460 (i.e., the controllably conductive has not latched), thecontroller416 determines that thelighting load202 is a dimmable screw-in compact fluorescent lamp, changes to the fluorescent operating mode, and adjusts the high-end intensity setting to the second high-end intensity setting value atstep464. If the manufacturer of the lamp (as stored in the memory318) is Philips atstep466, the low-end intensity setting is adjusted to the second low-end intensity setting value atstep468. Otherwise, the low-end intensity setting is adjusted to the third low-end intensity setting value atstep470. The user of the dimmer400 may also use the advanced programming mode to change the manufacturer of the fluorescent lamp (as shown inFIG. 18).

FIG. 22 is a simplified flowchart of acontrol procedure480 executed by thecontroller416 periodically, e.g., once every half-cycle of theAC power source12 in response to a zero-crossing of the AC line voltage atstep332. Thecontroller procedure480 is very similar to thecontrol procedure330 ofFIG. 16. However, after controlling thelighting load202 from off to on (i.e., atsteps342 and352), thecontroller416 determines whether the flag CHK_LOAD is set atstep482. If not, thecontrol procedure480 continues as normal to appropriately control the controllably conductive switching device atstep340. However, if the flag CHK_LOAD is set atstep482, thecontroller416 executes the operating mode update routine450 (FIG. 21) to automatically detect the type of lighting load connected to thedimmer switch400. The flag CHK_LOAD is then cleared atstep484, and thecontrol procedure480 exits.

Alternatively, thecontroller416 could execute the operatingmode update routine450 for multiple consecutive half-cycles, and adjust the operating mode of thedimmer switch400 based on the data produced from all of the multiple half-cycles.

Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.

Claims (21)

1. A two-wire dimmer circuit for a fluorescent lamp load including a ballast circuit, the two-wire dimmer circuit adapted to be coupled in series electrical connection between an AC power source and the ballast circuit, the two-wire dimmer control circuit comprising:

a triac having a holding current rating of less than 35 mA, the triac adapted to be coupled in series electrical connection between the AC power source and the ballast circuit for controlling the amount of power delivered to the ballast circuit, the triac having a control input;

a timing circuit operatively coupled in parallel electrical connection with the triac, the timing circuit having an output for generating a timing voltage representative of a desired intensity of the fluorescent lamp;

a trigger circuit comprising a first diac having a break-over voltage of approximately 30 V, the trigger circuit operatively coupled between the output of the timing circuit and the control input of the triac, the trigger circuit operable to render the triac conductive in response to the timing voltage, such that the triac is conductive for a conduction interval each half-cycle;

a filter circuit coupled in parallel electrical connection with the triac, the filter circuit comprising a filter resistor having a resistance of approximately 220 Ω in series with a filter capacitor having a capacitance of approximately 0.047 μF, the filter circuit operable to minimize ringing in a dimmed-hot voltage produced across the fluorescent lamp load; and

a voltage compensation circuit coupled in series electrical connection with the timing circuit, such that the series combination of the timing circuit and the voltage compensation circuit are coupled in parallel electrical connection with the triac, the voltage compensation circuit operable to compensate for voltage fluctuations of the AC power source, the voltage compensation circuit comprising:

a first resistor coupled in series electrical connection with two series-coupled diacs, the resistor having a resistance of approximately 27 kΩ, and the two series-coupled diacs both having break-over voltages of approximately 30 V, the junction of the first resistor and the two series-coupled diacs connected to the timing circuit;

wherein the timing circuit is adapted to limit the conduction interval to less than approximately 75% and greater than approximately 31% of each half-cycle, the timing circuit comprising:

a potentiometer having two main terminals and a wiper terminal coupled to one of the main terminals, such that the resistance of the potentiometer between the two main terminals ranges from approximately 0 Ω to 300 kΩ;

a high-end resistor coupled in series electrical connection with the main terminals of the potentiometer, the high-end resistor having a resistance greater than approximately 22 kΩ;

a firing capacitor coupled to the output of the timing circuit for generating the timing voltage, the firing capacitor adapted to charge through the potentiometer and the high-end resistor and having a capacitance of approximately 0.047 μF; and

a calibration resistor coupled in parallel electrical connection with the two main terminals of the potentiometer and having a resistance of approximately 110 kΩ.

2. The dimmer circuit ofclaim 1, wherein the high-end resistor has a resistance of approximately 44 kΩ.

3. The dimmer circuit ofclaim 1, wherein the low holding current rating is approximately 15 mA.

4. A dimmer switch adapted to be coupled between an AC power source and a lighting load for controlling the intensity of the lighting load between a high-end intensity setting and a low-end intensity setting, the dimmer switch comprising:

a user-accessible adjustment actuator for changing the dimmer switch between first and second operating modes, such that the high-end intensity setting is adjusted to a first high-end intensity setting value and the low-end intensity setting is adjusted to a first low-end intensity setting value in the first operating mode, and the high-end intensity setting is adjusted to a second high-end intensity setting value less than the first high-end intensity setting value, and the low-end intensity setting is adjusted to a second low-end intensity setting value greater than the first low-end intensity setting value in the second operating mode;

a controllably conductive switching device adapted to be coupled in series electrical connection between the AC power source and the lighting load, the controllably conductive switching device having a control input for controlling the controllably conductive switching device;

a trigger circuit coupled to the control input of the controllably conductive switching device for rendering the controllably conductive switching device conductive each half-cycle of the AC power source; and

a timing circuit operatively coupled in parallel electrical connection with the controllably conductive switching device for generating a timing voltage, the timing circuit comprising:

a potentiometer for providing a variable resistance;

a firing capacitor coupled to the output of the timing circuit for generating the timing voltage, the firing capacitor adapted to charge through the potentiometer;

a high-end resistor coupled in series electrical connection with the potentiometer, the firing capacitor adapted to charge through the potentiometer and the first high-end resistor;

a mechanical switch mechanically coupled to the user-accessible adjustment actuator and electrically coupled to the first high-end resistor, such that when the mechanical switch is in a first position, the dimmer switch operates in the first operating mode and a first resistance is provided in series with the potentiometer, and when the mechanical switch is in a second position, the dimmer switch operates in the second operating mode and a second resistance is provided in series with the potentiometer;

wherein the trigger circuit is operable to control the semiconductor switch in response to the timing voltage.

5. The dimmer switch ofclaim 4, wherein the timing circuit further comprises:

a first low-end resistor coupled in parallel electrical connection with the potentiometer;

wherein the mechanical switch is electrically coupled to the low-end resistor, such that a third resistance is provided in parallel with the potentiometer when the mechanical switch is in the first position, and a fourth resistance is provided in parallel with the potentiometer when the mechanical switch is in the second position.

6. The dimmer switch ofclaim 4, wherein the timing circuit further comprises:

a second high-end resistor coupled in series with the first high-end resistor, the series combination of the first and second high-end resistors coupled in series with the potentiometer; and

a second low-end resistor coupled in series with the first low-end resistor, the series combination of the first and second low-end resistors coupled in parallel with the potentiometer;

wherein the mechanical switch is coupled such that one of the first and second high-end resistors is electrically shorted when the mechanical switch is in a first position, and one of the first and second low-end resistors is electrically shorted when the mechanical switch is in a second position.

7. The dimmer switch ofclaim 6, wherein the mechanical switch comprises a single-pole double-throw switch.

8. The dimmer switch ofclaim 4, further comprising:

an intensity adjustment actuator mechanically coupled to the potentiometer, such that the variable resistance of the potentiometer is responsive to the intensity adjustment actuator.

9. A drive circuit for a controllably conductive switching device of a dimmer switch adapted to be coupled between an AC power source and a lighting load for controlling the intensity of the lighting load between a high-end intensity setting and a low-end intensity setting, the drive circuit comprising:

a potentiometer for providing a variable resistance;

a firing capacitor coupled to an output of the potentiometer for generating a timing voltage, the firing capacitor adapted to charge through the potentiometer such that the timing voltage is responsive to the variable resistance of the potentiometer;

first and second high-end resistors coupled in series, such that the series combination of the first and second high-end resistors are coupled in series with the potentiometer;

first and second low-end resistors coupled in series, such that the series combination of the first and second low-end resistors are coupled in parallel with the potentiometer; and

a mechanical switch for changing the dimmer switch between first and second operating modes, such that the high-end intensity setting is adjusted to a first high-end intensity setting value and the low-end intensity setting is adjusted to a first low-end intensity setting value in the first operating mode, and the high-end intensity setting is adjusted to a second high-end intensity setting value and the low-end intensity setting is adjusted to a second low-end intensity setting value in the second operating mode, the second high-end intensity setting value less than the first high-end intensity setting value, and the second low-end intensity setting value greater than the first low-end intensity setting value,

wherein the mechanical switch is coupled such that one of the first and second high-end resistors is electrically shorted when the mechanical switch is in a first position, and one of the first and second low-end resistors is electrically shorted when the mechanical switch is in a second position.

10. The drive circuit ofclaim 9, wherein the mechanical switch comprises a single-pole double-throw switch.

11. A dimmer switch adapted to be coupled between an AC power source generating an AC line voltage and a lighting load for controlling the intensity of the lighting load between a high-end intensity setting and a low-end intensity setting, the dimmer switch comprising:

a controllably conductive switching device adapted to be coupled in series electrical connection between the AC line voltage and the lighting load for controlling the amount of power delivered to the lighting load, the controllably conductive switching device having a conductive state and a non-conductive state;

a controller operable to drive the controllably conductive switching device to change the controllably conductive switching device from the non-conductive state to the conductive state each half-cycle of the AC power source, the controller operable to render the controllably conductive switching device conductive after a minimum off time following a zero-crossing of the AC line voltage, and to subsequently determine whether the controllably conductive switching device is conducting a load current to the lighting load; and

a voltage detect circuit coupled in parallel electrical connection with the controllably conductive switching device, the voltage detect circuit operable to provide a control signal representative of the magnitude of a voltage across the controllably conductive switching device to the controller;

wherein the controller is operable to adjust the dimmer switch to one of a first operating mode and a second operating mode in response to whether the controllably conductive switching device is conducting current to the load, the controller operable to adjust the high-end intensity setting to a first high-end intensity setting value and the low-end intensity setting to a first low-end intensity setting value in the first operating mode, and to set the high-end intensity setting to a second high-end intensity setting value less than the first high-end intensity setting value, and the low-end intensity setting to a second low-end intensity setting value greater than the first low-end intensity setting value in the second operating mode.

12. The dimmer switch ofclaim 11, wherein the controller is operable to determine the magnitude of the voltage across the controllably conductive switching device at a predetermined time after the controller renders the controllably conductive switching device conductive.

13. The dimmer switch ofclaim 12, wherein the controller is operable to adjust the dimmer switch to the second operating mode if the voltage across the controllably conductive switching device is greater than a predetermined voltage threshold at the predetermined time after the controller renders the controllably conductive switching device conductive.

14. The dimmer switch ofclaim 13, wherein the predetermined voltage threshold comprises approximately 2 volts.

15. The dimmer switch ofclaim 13, wherein the first and second operating modes comprise an incandescent operating mode and a screw-in compact fluorescent operating mode, respectively.

16. The dimmer switch ofclaim 12, wherein the controller is operable to adjust the dimmer switch to the first operating mode if the voltage across the controllably conductive switching device is less than a predetermined voltage threshold.

17. The dimmer switch ofclaim 12, wherein the predetermined time comprises 400 μsec.

18. A dimmer switch adapted to be coupled between an AC power source generating an AC line voltage and a lighting load for controlling the intensity of the lighting load between a high-end intensity setting and a low-end intensity setting, the dimmer switch comprising:

a controllably conductive switching device adapted to be coupled in series electrical connection between the AC line voltage and the lighting load for controlling the amount of power delivered to the lighting load, the controllably conductive switching device having a conductive state and a non-conductive state;

a controller operable to drive the controllably conductive switching device to change the controllably conductive switching device from the non-conductive state to the conductive state each half-cycle of the AC power source, the controller operable to render the controllably conductive switching device conductive after a minimum off time following a zero-crossing of the AC line voltage, and to subsequently determine whether the controllably conductive switching device is conducting a load current to the lighting load; and

a sensing circuit operable to sense an electrical characteristic representative of a magnitude of the load current, the controller coupled to the sensing circuit, such that the controller is operable to adjust the dimmer switch to one of a first operating mode and a second operating mode in response to the electrical characteristic;

wherein the controller is further operable to adjust the dimmer switch to one of the first operating mode and the second operating mode in response to whether the controllably conductive switching device is conducting current to the load, the controller operable to adjust the high-end intensity setting to a first high-end intensity setting value and the low-end intensity setting to a first low-end intensity setting value in the first operating mode, and to set the high-end intensity setting to a second high-end intensity setting value less than the first high-end intensity setting value, and the low-end intensity setting to a second low-end intensity setting value greater than the first low-end intensity setting value in the second operating mode.

19. A dimmer switch adapted to be coupled between an AC power source generating an AC line voltage and a lighting load for controlling the intensity of the lighting load between a high-end intensity setting and a low-end intensity setting, the dimmer switch comprising:

a controllably conductive switching device adapted to be coupled in series electrical connection between the AC line voltage and the lighting load for controlling the amount of power delivered to the lighting load, the controllably conductive switching device having a conductive state and a non-conductive state; and

a controller operable to drive the controllably conductive switching device to change the controllably conductive switching device from the non-conductive state to the conductive state each half-cycle of the AC power source, the controller operable to render the controllably conductive switching device conductive after a minimum off time following a zero-crossing of the AC line voltage, and to subsequently determine whether the controllably conductive switching device is conducting a load current to the lighting load;

wherein the controller is further operable to adjust the dimmer switch to one of the first operating mode and the second operating mode in response to whether the controllably conductive switching device is conducting current to the load, the controller operable to adjust the high-end intensity setting to a first high-end intensity setting value and the low-end intensity setting to a first low-end intensity setting value in the first operating mode, and to set the high-end intensity setting to a second high-end intensity setting value less than the first high-end intensity setting value, and the low-end intensity setting to a second low-end intensity setting value greater than the first low-end intensity setting value in the second operating mode; and wherein the controller is further operable to adjust the dimmer switch to one of the first operating mode and the second operating mode at power-up of the controller.

20. The dimmer switch ofclaim 19, further comprising:

a memory coupled to the controller for storing a desired intensity of the lighting load;

wherein the controller is operable to determine the desired intensity from the memory at power-up of the controller, and to adjust the dimmer switch to one of the first operating mode and the second operating mode at power-up if the desired intensity is greater than zero.

21. The dimmer switch ofclaim 20, further comprising:

a control actuator coupled to the controller, the controller operable to turn the lighting load on in response to an actuation of the control actuator;

wherein, if the desired intensity is determined to be off at power-up, the controller is operable to adjust the dimmer switch to one of the first operating mode and the second operating mode when the lighting load is turned on.

Images